<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<frameset rows="50%,50%">

    <frame src="a.html">

    <frameset cols="25%,75%">
        <frame src="b.html">
        <frame src="c.html">
    </frameset>

    <noframes>您的浏览器无法处理框架！</noframes>
</frameset>

</body>
</html>